Suppressor T-cells play an important role in the biology of human tumors. The focus of the work we propose is the suppressor T-cell subset which is characterized by the possession of a surface receptor for histamine of the H2 type (H2R plus cells). Previously we have studied this cell from biochemical and immunological perspectives. This has included the solubilization and partial purification of the specific histamine H2 receptor as well as the description of the histamine activation of the cell to a functional suppressor lymphocyte. Our work is a detailed study of the relationship of this specific suppressor cell to malignant disease. In order to do so we will characterize and quantitate histamine receptors on the T-cells of patients and animals with malignant disease; determine the effect of histamine and its antagonists on the functional immunological activity of the H2R plus cell; determine if histamine and its antagonists have a role in the therapy of cancer; and determine the role that serum histamine has in the pathophysiology of malignancies.